In computer systems, for example, it is known practice to arrange a plurality of memory components, for instance, in the form of “DRAMs” (Dynamic Random Access Memories), on a common mounting substrate. Memory arrangements of this type are known, in particular, as “DIMMs” (Registered or Buffered Dual Inline Memory Modules). “DIMMS” are typically fitted with 16 or 18 memory chips, which are clock-controlled when of “SDRAMs” or “DDR DRAMs”.
An integrated dynamic memory in the form of a DRAM generally has a memory cell array which comprises word lines and bit lines. In this case, the memory cells are arranged at crossover points between the bit lines and word lines. In particular, the memory cells have a storage capacitor and a selection transistor, with the selection transistor connecting the associated storage capacitor to one of the bit lines. Control connections on the respective selection transistors are respectively connected to one of the word lines for the purpose of selecting the memory cells. An activated word line turns on respective connected selection transistors, in which case, following the selection of a word line, data signals from the memory cells along the selected word line are applied to the corresponding bit lines. A data signal from a selected memory cell is assessed and amplified in a sense amplifier in the memory cell array. In the case of read access, the data signals from selected memory cells are read out for the purpose of further processing, and in the case of write access, data signals to be written are written to the selected memory cells.
In the case of integrated dynamic memories of this type, a “refresh mode” is required, at times of operation at which the memory cells are not being externally accessed, to refresh and thus permanently retain the memory cell contents, which may vanish, for example, as a result of leakage currents in the storage capacitor or selection transistor. In the refresh mode, the assessed and amplified data signals from selected memory cells are written back directly to the memory cells in question.
Integrated memories such as DRAMs are used in data processing systems such as, for example, computer systems, where they are driven, for example, by a microprocessor or microcontroller. In this case, a memory module in the form of a DIMM is arranged in a known manner, for example, in a slot in a “motherboard” in the computer system, and communicates with the microprocessor or microcontroller via corresponding conductor tracks on the motherboard. In order to initiate a refresh sequence in a memory on a DIMM, which is operated in this manner, an external command, for instance an “autorefresh” command, is normally required. The command is periodically applied by the microprocessor or microcontroller, for example, in the form of a memory controller. In order to be able to achieve a functionality of this type, it is necessary to equip the microprocessor or microcontroller with appropriate registers or switching mechanisms. However, this generally increases the design complexity of a chip of this type.